MAPREDUCE-6105. nconsistent configuration in property mapreduce.reduce.shuffle.merge.percent. Contributed by Ray Chiang.

hadoop-mapreduce-project/CHANGES.txt

@@ -253,6 +253,9 @@ Release 2.8.0 - UNRELEASED
 
   IMPROVEMENTS
 
+    MAPREDUCE-6105. Inconsistent configuration in property
+    mapreduce.reduce.shuffle.merge.percent. (Ray Chiang via harsh)
+
     MAPREDUCE-4414. Add main methods to JobConf and YarnConfiguration,
     for debug purposes. (Plamen Jeliazkov via harsh)
 

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/MRJobConfig.java

@@ -305,6 +305,7 @@ public interface MRJobConfig {
     = "mapreduce.reduce.shuffle.memory.limit.percent";
 
   public static final String SHUFFLE_MERGE_PERCENT = "mapreduce.reduce.shuffle.merge.percent";
+  public static final float DEFAULT_SHUFFLE_MERGE_PERCENT = 0.66f;
 
   public static final String REDUCE_FAILURES_MAXPERCENT = "mapreduce.reduce.failures.maxpercent";
 

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/task/reduce/MergeManagerImpl.java

@@ -191,8 +191,9 @@ public class MergeManagerImpl<K, V> implements MergeManager<K, V> {
     this.memToMemMergeOutputsThreshold = 
             jobConf.getInt(MRJobConfig.REDUCE_MEMTOMEM_THRESHOLD, ioSortFactor);
     this.mergeThreshold = (long)(this.memoryLimit * 
-                          jobConf.getFloat(MRJobConfig.SHUFFLE_MERGE_PERCENT, 
-                                           0.90f));
+                          jobConf.getFloat(
+                            MRJobConfig.SHUFFLE_MERGE_PERCENT,
+                            MRJobConfig.DEFAULT_SHUFFLE_MERGE_PERCENT));
     LOG.info("MergerManager: memoryLimit=" + memoryLimit + ", " +
              "maxSingleShuffleLimit=" + maxSingleShuffleLimit + ", " +
              "mergeThreshold=" + mergeThreshold + ", " +